The present invention relates generally to power generating plants, and more particularly, to a power generation plant such as, for example, a combined-cycle power plant that incorporates a thermal energy storage unit to supplement or boost steam production and power output.
In a typical operation of a combined-cycle power plant where exhaust energy generated from a gas turbine is used to power a steam turbine, the power output generated from the plant will depend on the period of the day and the load associated therewith. For example, in the early morning hours, the demand for energy is generally lower than other periods in the day, and thus the combined-cycle power plant will operate at a minimum plant turndown load. As the demand for energy increases from these early morning hours, the combined-cycle power plant will ramp up power output to a base load. There will be certain times in the day when the demand for energy peaks. During these peak-demand periods, the thermal efficiency of the combined-cycle power plant will be reduced as power output is increased to meet the peak load. Some combined-cycle power plants utilize duct firing to generate the additional power output to meet the increased demand for energy during these peak-demand periods. Duct firing is inherently a less efficient method of power generation, so the combined-cycle power plant will operate at a thermal efficiency that is less than desirable.